1. Field of the Invention
The present invention relates to a communication navigation system and a communication navigation method for vehicle use or the like, which can perform navigation processing, such as route search, route navigation, map display, and the like, at least partially by using a communication network, as well as a program storage device and a computer data signal embodiment in a carrier wave.
2. Description of the Related Art
Nowadays, research and development on electronic control for controlling the drive of a vehicle are advanced, and navigation systems for aiding in driving are significantly spread and popularized. This navigation system generally has various databases and such a basic structure that displays, on a display device, map information, current position information, various guidance information, and the like. Moreover, it searches for a drive route on the basis of an inputted condition.
A function called as a “route search” or “path search” of a navigation apparatus mounted on a vehicle is designed to be capable of searching for an optimum route connecting an origin and a destination, both of which are designated by a user. It is also designed to lead and guide (navigate) the user to the destination by displaying on a map a current position based on a self-contained or built-in positioning measurement or a GPS (Global Positioning System) measurement and the searched optimum route.
With respect to a traditional navigation apparatus, this kind of route search is performed by microprocessor processing in the apparatus on the basis of the map database information stored in a map information record medium (e.g. a DVD-ROM) equipped in the navigation apparatus. More concretely, the route search is executed by using “information for a route search”, which enables a search for the optimum route based on predetermined mathematical algorithm, such as link information corresponding to a road part between branching points and intersections, node information including coordinates information (e.g., absolute position information on latitude and longitude, or on altitude, latitude and longitude) corresponding to the branching points and the intersections of roads or the like among the map database information. Generally, in view of its nature of being for route search, this kind of information for a route search is constructed by the link information, the node information, and the like, which are about broad areas where roads are mutually connected, for example, such as throughout Honshu or the main island of Japan, throughout Japan, or the like, so that its volume of data becomes enormous, which increases the whole amount of data of the map database information.
Moreover, the map database information includes data of added information, which may be facility guidance information on tourist attractions/facilities, facility numerals, names (characters) of maps/roads, views of waters/railroads, and roads, in each one of many pieces of map information (drawings). These data as well as the above-described information for the route search further increase the volume of data of the map database information.
By the way, the search for the optimum route requires the newest map database information because of changes, new constructions, and the like on roads.
Therefore, there is a need to equip for the traditional navigation apparatus a map information record medium that stores the map database information which is the newest and whose data volume is enormous. At the same time, there is a need of the display processing and the search processing of the optimum route based on the complicated map database information. In this case, there is a need to mount a microprocessor unit (MPU), which is capable of high-speed processing, so that the scale of the processing and that of the apparatus come to increase.
On that account, various communication navigation systems are suggested in order to improve such increase of the scale of the processing and that of the apparatus. In these communication navigation systems, the map database information is obtained and provided through two-way wireless communication between a communication center apparatus on a communication network and a communication navigation terminal mounted on a vehicle (e.g. refer to the examples of Japanese Patent Application Laying Open NO. Hei 7-262493 “a system for distributing map information for a movable body” and Japanese Patent Application Laying Open NO. Hei 10-96644 “a system for guiding a moving route”).
The communication center apparatus in the communication navigation system in this kind can quickly and cheaply provide the newest map database information, because, for example, all we need is update the map database information of one communication center apparatus to the newest information, comparing to the case of providing an information record medium, which stores the newest map database information, for an individual navigation apparatus mounted on a movable body. Therefore, users side becomes able to receive the map database information including the newest information for the route search or the like.
Moreover, there has been developed such a communication navigation system that is designed not to perform the route search on the side of the communication navigation terminal, but to transmit information indicating a current position or an origin and a destination on the side of the communication navigation terminal, to perform the route search according to these by a high performance processor on the side of the communication center apparatus, to receive this search result and display it in a predetermined format on the side of the communication navigation terminal and so on.
However, the above-described communication navigation system has the following disadvantage.
It is impossible to have a service of navigation in the area that an electric wave cannot arrive in with a sufficient electric field intensity to use a wireless device. Usually, in this situation, there is no problem while driving along a route of a preset drive plan, however, in the case of deviating from the route by some reasons, if the area is out of a service area, it becomes impossible to obtain information to return the original route. For example, if it is impossible to transmit and receive the necessary information for the route search, then it is impossible to perform a route search to return to the route from which the movable body has deviated (hereinafter, such a route search is referred to as a “reroute search” as the occasion demands) on the side of the communication navigation terminal. Alternatively, if it is impossible to receive information on a current position or the like, then it is impossible to perform the reroute search on the side of the communication center apparatus. Moreover, if it is impossible to transmit and receive the search result, there is no meaning to perform the reroute search. Particularly, a movable body communication network is placed along expressways and main highways in many cases, and once the movable body deviates from this road, it is impossible to communicate, which is sufficiently assumed. Moreover, in the current situation, the infrastructure of a communication device such as a cellular phone or the like is not sufficiently promoted in mountain areas, and even in the future, it is difficult to think of the possibility to promote the infrastructure to cover all districts including depopulated areas, in the view of economic investment efficiency.
On that account, it is extremely important to construct a device for executing some navigation processing, such as searching for a route or a direction to be traveled, providing the search result, and the like, even if a vehicle enters into the area that it cannot communicate from its communication terminal, when expanding the use of the communication navigation system.